1. Field of the Invention
The present invention relates to a liquid crystal display for displaying images on the basis of input video signals, and more particularly to a liquid crystal display in which start timing for writing a liquid crystal is improved.
2. Background Art
In general, when an image is displayed on a liquid crystal display (LCD), image signals are output from a graphics controller in a system unit or system part of a PC or the like (i.e., host's side) via a video interface. An LCD controller LSI, which receives these image signals, supplies signals to each IC in a source driver (i.e., X driver, LCD source driver) and gate driver (i.e., Y driver), and then a voltage is applied to each source electrode and each gate electrode in a TFT array arranged in a matrix fashion, thereby leading to displaying images. As a mounting and wiring scheme employed in this LCD source driver, technologies called chip-on-glass (COG) and wiring-on-array (WOA) have recently become the focus of attention. Also, a technology is being developed where a driver LSI is arranged in a TCP (tape carrier package) and connected to the TFT array substrate (glass substrate) via the TCP. It is expected that manufactures' costs will be greatly reduced by applying these technologies to attach ICs directly on the glass substrate or via the TCP as well as to eliminate wiring on a printed circuit board.
FIGS. 21(a) and (b) shows an example of wiring for source drivers and measured current results on the power supply line when writing the liquid crystal simultaneously. In the wiring for source drivers shown in FIG. 21(a), video signals, control signals and power supply lines are connected via bus to a plurality of LCD source drivers 201. The start timing for writing the liquid crystal (TFT array) is controlled by the LCD controller (not shown) activating the output start signal 202, wherein all of the mounted LCD source drivers 201 start writing of the liquid crystal simultaneously. At this time, there occurs a spike current on the order of several hundreds milliamperes on the power supply line as shown in FIG. 21(b).
Conventionally, the wiring between the LCD source drivers 201 has been implemented as copper wiring on the PCB (printed circuit board) or FPC (flexible printed circuit). On the other hand, for the above-mentioned COG and WOA technologies, LCD source drivers 201 are mounted directly on the TFT array substrate and the wiring between LCD source drivers 201 is implemented by means of aluminum or the like on the substrate by employing the TFT array process. In this case, the aluminum wiring on the TFT array substrate is limited to about 2500Å in thickness in order to improve the manufacturing yield and to reduce process time occupied. This does not allow an adequate current capacity so that the problem has occurred that the power supply line blows when several hundreds milliamperes of spike current flows as shown in FIG. 21(b). Namely, the power supply lines on the PCBs or FPCs according to the prior art can assure the adequate current capacities so that no blowing of the power supply lines has occurred, while when employing the COG or WOA technologies, blowing of the power supply lines formed on the glass might occur.
Moreover, for the LCD panels where the power supply lines are formed on the PCBs or FPCs, there has been no problem about voltage drop due to the wiring. However, when employing COG or WOA technologies, the voltage drop over the power supply lines increases because it is difficult to implement power supply lines that have adequate current capacities, as described above. When this voltage drop increases, the supply voltage for LCD source drivers 201 decreases, which causes the delay of writing of the liquid crystal. Consequently, the writing voltage for each of the LCD source drivers 201 differs depending on the positions of them in terms of distance from the portal of the power supply (e.g., either the upstream side close to the power source or the downstream side far away from the power source), which results in degrading the uniformity of image qualities.